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AcSIR Ph.D Thesis Colloquium of Ms. Silpa K AcSIR Reg.No.10PP14J45002 
Monday, 29 June 2020,  3:00 -  5:00
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ABSTRACT

The lithospheric stress accumulated due to relative plate motions are mostly accommodated at plate boundary fault interface zones and is evident from dense and destructive seismic activity there. Unlike these plate interface earthquakes, there are infrequent large intraplate event occurrences within the continental/oceanic interiors and sinking slabs, and this study, in particular, looks at their seismogenic characteristics. These earthquakes can be highly destructive owing to their shallow source, generate a very high amount of ground shaking and can occur as a complete surprise at regions with no known seismic history, etc. Interestingly, at times these class of events is reported from regions where strain rates are considered to be low, yet destructive. Of and on, very large magnitude earthquakes with complex slip histories are also globally observed. It is also observed that these within the plate earthquakes can also be associated with the earthquake cycles of the plate boundary structures in the vicinity. With this background, this study particularly focuses on the Indian plate intraplate deformation, paying attention towards its stable continental region (SCR), diffuse Wharton zone, outer-rise region of the Andaman Nicobar subduction and sinking slab interiors of the Indo-Burmese, Himalayan collision regions. The mode of investigation involved the usage of the tele-seismic kinematic finite-fault simulations with supportive stress-inversion models.

Results on the Indian SCR region indicate seismogenic features with compact singular asperity breakage within the Indian crust with faulting at younger structures or heterogeneous slip planes with varying fault maturity and roughness. Likewise, Northern Wharton diffuse basin models favour faulting on ∼ESE-WNW oriented active shear structures. This study confirms that the centroid depths at this region lie within the 600 0 C isotherm, but occasionally the seismic slip can extend up to ∼750 0 C isotherm, indicating brittle nature at the upper mantle. A depth-wise variation in stress field with shallow oblique-normal faulting and deeper oblique-reverse, indicating plate bending or slip-partitioning effects having direct control on the Northern Wharton tectonics. Similar analysis on the outer-rise region of Andaman-Nicobar subduction revealed active deformation due to slab bending effects and the possible influence of northward drag of Indian plate stresses at North, South and Little Andaman regions. Models indicate extensive stress field rotations after the 2004 Mw 9.2 megathrust earthquake and have resulted in a mixed response of seismicity within the slab as well as the nearby Wharton Basin. Co-seismic and post-seismic model comparisons have indicated a strong correlation with zones of co-seismic stress relief and regions of rapid post-seismic reloading. Similarly, arc-parallel stretching or buttressing effects are inferred as the reason for the lower crustal to upper mantle earthquakes in Sikkim Himalaya and Indo-Burmese slab deformation respectively.

ALL ARE WELCOME

N.B.: Head, CSIR-4PI desires that COVID-19 norms be strictly followed in the conference hall while

attending the colloquium. Requests to be seated in alternate rows and seats, wearing masks.

Location Conference Hall, Network Building, CSIR Fourth Paradigm Institute

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